/* GTK - The GIMP Toolkit
 * Copyright (C) 2017, Red Hat, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 *
 * Author(s): Carlos Garnacho <carlosg@gnome.org>
 */

/**
 * GtkEventControllerScroll:
 *
 * `GtkEventControllerScroll` is an event controller that handles scroll
 * events.
 *
 * It is capable of handling both discrete and continuous scroll
 * events from mice or touchpads, abstracting them both with the
 * [signal@Gtk.EventControllerScroll::scroll] signal. Deltas in
 * the discrete case are multiples of 1.
 *
 * In the case of continuous scroll events, `GtkEventControllerScroll`
 * encloses all [signal@Gtk.EventControllerScroll::scroll] emissions
 * between two [signal@Gtk.EventControllerScroll::scroll-begin] and
 * [signal@Gtk.EventControllerScroll::scroll-end] signals.
 *
 * The behavior of the event controller can be modified by the flags
 * given at creation time, or modified at a later point through
 * [method@Gtk.EventControllerScroll.set_flags] (e.g. because the scrolling
 * conditions of the widget changed).
 *
 * The controller can be set up to emit motion for either/both vertical
 * and horizontal scroll events through %GTK_EVENT_CONTROLLER_SCROLL_VERTICAL,
 * %GTK_EVENT_CONTROLLER_SCROLL_HORIZONTAL and %GTK_EVENT_CONTROLLER_SCROLL_BOTH_AXES.
 * If any axis is disabled, the respective [signal@Gtk.EventControllerScroll::scroll]
 * delta will be 0. Vertical scroll events will be translated to horizontal
 * motion for the devices incapable of horizontal scrolling.
 *
 * The event controller can also be forced to emit discrete events on all
 * devices through %GTK_EVENT_CONTROLLER_SCROLL_DISCRETE. This can be used
 * to implement discrete actions triggered through scroll events (e.g.
 * switching across combobox options).
 *
 * The %GTK_EVENT_CONTROLLER_SCROLL_KINETIC flag toggles the emission of the
 * [signal@Gtk.EventControllerScroll::decelerate] signal, emitted at the end
 * of scrolling with two X/Y velocity arguments that are consistent with the
 * motion that was received.
 */
#include "config.h"

#include "gtkwidget.h"
#include "gtkeventcontrollerprivate.h"
#include "gtkeventcontrollerscroll.h"
#include "gtktypebuiltins.h"
#include "gtkmarshalers.h"
#include "gtkprivate.h"

#define SCROLL_CAPTURE_THRESHOLD_MS 150
#define HOLD_TIMEOUT_MS 50
#define SURFACE_UNIT_DISCRETE_MAPPING 10

typedef struct
{
  double dx;
  double dy;
  guint32 evtime;
} ScrollHistoryElem;

struct _GtkEventControllerScroll
{
  GtkEventController parent_instance;
  GtkEventControllerScrollFlags flags;
  GArray *scroll_history;

  /* For discrete event coalescing */
  double cur_dx;
  double cur_dy;
  double last_cur_dx;
  double last_cur_dy;

  GdkScrollUnit cur_unit;

  guint hold_timeout_id;
  guint active : 1;
};

struct _GtkEventControllerScrollClass
{
  GtkEventControllerClass parent_class;
};

enum {
  SCROLL_BEGIN,
  SCROLL,
  SCROLL_END,
  DECELERATE,
  N_SIGNALS
};

enum {
  PROP_0,
  PROP_FLAGS,
  N_PROPS
};

static GParamSpec *pspecs[N_PROPS] = { NULL };
static guint signals[N_SIGNALS] = { 0 };

G_DEFINE_TYPE (GtkEventControllerScroll, gtk_event_controller_scroll,
               GTK_TYPE_EVENT_CONTROLLER)

static void
scroll_history_push (GtkEventControllerScroll *scroll,
                     double                    delta_x,
                     double                    delta_y,
                     guint32                   evtime)
{
  ScrollHistoryElem new_item;
  guint i;

  for (i = 0; i < scroll->scroll_history->len; i++)
    {
      ScrollHistoryElem *elem;

      elem = &g_array_index (scroll->scroll_history, ScrollHistoryElem, i);

      if (elem->evtime >= evtime - SCROLL_CAPTURE_THRESHOLD_MS)
        break;
    }

  if (i > 0)
    g_array_remove_range (scroll->scroll_history, 0, i);

  new_item.dx = delta_x;
  new_item.dy = delta_y;
  new_item.evtime = evtime;
  g_array_append_val (scroll->scroll_history, new_item);
}

static void
scroll_history_reset (GtkEventControllerScroll *scroll)
{
  if (scroll->scroll_history->len == 0)
    return;

  g_array_remove_range (scroll->scroll_history, 0,
                        scroll->scroll_history->len);
}

static void
scroll_history_finish (GtkEventControllerScroll *scroll,
                       double                   *velocity_x,
                       double                   *velocity_y)
{
  double accum_dx = 0, accum_dy = 0;
  guint32 first = 0, last = 0;
  guint i;

  *velocity_x = 0;
  *velocity_y = 0;

  if (scroll->scroll_history->len == 0)
    return;

  for (i = 0; i < scroll->scroll_history->len; i++)
    {
      ScrollHistoryElem *elem;

      elem = &g_array_index (scroll->scroll_history, ScrollHistoryElem, i);
      accum_dx += elem->dx;
      accum_dy += elem->dy;
      last = elem->evtime;

      if (i == 0)
        first = elem->evtime;
    }

  if (last != first)
    {
      *velocity_x = (accum_dx * 1000) / (last - first);
      *velocity_y = (accum_dy * 1000) / (last - first);
    }

  scroll_history_reset (scroll);
}

static void
gtk_event_controller_scroll_finalize (GObject *object)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (object);

  g_array_unref (scroll->scroll_history);
  g_clear_handle_id (&scroll->hold_timeout_id, g_source_remove);

  G_OBJECT_CLASS (gtk_event_controller_scroll_parent_class)->finalize (object);
}

static void
gtk_event_controller_scroll_set_property (GObject      *object,
                                          guint         prop_id,
                                          const GValue *value,
                                          GParamSpec   *pspec)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (object);

  switch (prop_id)
    {
    case PROP_FLAGS:
      gtk_event_controller_scroll_set_flags (scroll, g_value_get_flags (value));
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
    }
}

static void
gtk_event_controller_scroll_get_property (GObject    *object,
                                          guint       prop_id,
                                          GValue     *value,
                                          GParamSpec *pspec)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (object);

  switch (prop_id)
    {
    case PROP_FLAGS:
      g_value_set_flags (value, scroll->flags);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
    }
}

static void
gtk_event_controller_scroll_begin (GtkEventController *controller)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (controller);

  if (scroll->active)
    return;

  g_signal_emit (controller, signals[SCROLL_BEGIN], 0);
  scroll_history_reset (scroll);
  scroll->active = TRUE;
}

static void
gtk_event_controller_scroll_end (GtkEventController *controller)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (controller);

  if (!scroll->active)
    return;

  g_signal_emit (controller, signals[SCROLL_END], 0);
  scroll->active = FALSE;

  if (scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_KINETIC)
    {
      double vel_x, vel_y;

      scroll_history_finish (scroll, &vel_x, &vel_y);
      g_signal_emit (controller, signals[DECELERATE], 0, vel_x, vel_y);
    }
}

static gboolean
gtk_event_controller_scroll_hold_timeout (gpointer user_data)
{
  GtkEventController *controller;
  GtkEventControllerScroll *scroll;

  controller = user_data;
  scroll = GTK_EVENT_CONTROLLER_SCROLL (controller);

  gtk_event_controller_scroll_end (controller);
  scroll->hold_timeout_id = 0;

  return G_SOURCE_REMOVE;
}

static gboolean
gtk_event_controller_scroll_handle_hold_event (GtkEventController *controller,
                                               GdkEvent           *event)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (controller);
  GdkTouchpadGesturePhase phase;
  guint n_fingers = 0;

  if (gdk_event_get_event_type (event) != GDK_TOUCHPAD_HOLD)
    return GDK_EVENT_PROPAGATE;

  n_fingers = gdk_touchpad_event_get_n_fingers (event);
  if (n_fingers != 1 && n_fingers != 2)
    return GDK_EVENT_PROPAGATE;

  if (scroll->hold_timeout_id != 0)
    return GDK_EVENT_PROPAGATE;

  phase = gdk_touchpad_event_get_gesture_phase (event);

  switch (phase)
    {
    case GDK_TOUCHPAD_GESTURE_PHASE_BEGIN:
      gtk_event_controller_scroll_begin (controller);
      break;

    case GDK_TOUCHPAD_GESTURE_PHASE_END:
      gtk_event_controller_scroll_end (controller);
      break;

    case GDK_TOUCHPAD_GESTURE_PHASE_CANCEL:
      if (scroll->hold_timeout_id == 0)
        {
          scroll->hold_timeout_id =
              g_timeout_add (HOLD_TIMEOUT_MS,
                             gtk_event_controller_scroll_hold_timeout,
                             controller);
        }
      break;

    case GDK_TOUCHPAD_GESTURE_PHASE_UPDATE:
    default:
      break;
    }

  return GDK_EVENT_PROPAGATE;
}

static gboolean
should_reset_discrete_acc (double current_delta,
                           double last_delta)
{
  if (last_delta == 0)
    return TRUE;

  return (current_delta < 0 && last_delta > 0) ||
         (current_delta > 0 && last_delta < 0);
}

static gboolean
gtk_event_controller_scroll_handle_event (GtkEventController *controller,
                                          GdkEvent           *event,
                                          double              x,
                                          double              y)
{
  GtkEventControllerScroll *scroll = GTK_EVENT_CONTROLLER_SCROLL (controller);
  GdkScrollDirection direction = GDK_SCROLL_SMOOTH;
  double dx = 0, dy = 0;
  gboolean handled = GDK_EVENT_PROPAGATE;
  GdkEventType event_type;
  GdkScrollUnit scroll_unit;

  event_type = gdk_event_get_event_type (event);

  if (event_type == GDK_TOUCHPAD_HOLD)
    return gtk_event_controller_scroll_handle_hold_event (controller, event);

  if (event_type != GDK_SCROLL)
    return FALSE;

  if ((scroll->flags & (GTK_EVENT_CONTROLLER_SCROLL_VERTICAL |
                        GTK_EVENT_CONTROLLER_SCROLL_HORIZONTAL)) == 0)
    return FALSE;

  g_clear_handle_id (&scroll->hold_timeout_id, g_source_remove);

  scroll_unit = gdk_scroll_event_get_unit (event);

  /* FIXME: Handle device changes */
  direction = gdk_scroll_event_get_direction (event);
  if (direction == GDK_SCROLL_SMOOTH)
    {
      gdk_scroll_event_get_deltas (event, &dx, &dy);
      gtk_event_controller_scroll_begin (controller);

      if ((scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_VERTICAL) == 0)
        dy = 0;
      if ((scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_HORIZONTAL) == 0)
        dx = 0;

      if (scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_DISCRETE)
        {
          int steps;

          scroll->cur_dx += dx;
          scroll->cur_dy += dy;
          dx = dy = 0;

          if (scroll_unit == GDK_SCROLL_UNIT_SURFACE)
            {
              dx = (int) scroll->cur_dx / SURFACE_UNIT_DISCRETE_MAPPING;
              scroll->cur_dx -= dx * SURFACE_UNIT_DISCRETE_MAPPING;

              dy = (int) scroll->cur_dy / SURFACE_UNIT_DISCRETE_MAPPING;
              scroll->cur_dy -= dy * SURFACE_UNIT_DISCRETE_MAPPING;

              scroll_unit = GDK_SCROLL_UNIT_WHEEL;
            }
          else
            {
              if (ABS (scroll->cur_dx) >= 0.5)
                {
                  steps = trunc (scroll->cur_dx);
                  if (steps == 0)
                    steps = (scroll->cur_dx > 0) ? 1 : -1;

                  scroll->cur_dx -= steps;
                  dx = steps;
                }

              if (ABS (scroll->cur_dy) >= 0.5)
                {
                  steps = trunc (scroll->cur_dy);
                  if (steps == 0)
                    steps = (scroll->cur_dy > 0) ? 1 : -1;

                  scroll->cur_dy -= steps;
                  dy = steps;
                }
            }
        }
    }
  else
    {
      gdk_scroll_event_get_deltas (event, &dx, &dy);

      if ((scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_VERTICAL) == 0)
        dy = 0;
      if ((scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_HORIZONTAL) == 0)
        dx = 0;

      if (scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_DISCRETE)
        {
          int steps;

          if (dx != 0)
            {
              if (should_reset_discrete_acc (dx, scroll->last_cur_dx))
                scroll->cur_dx = 0;

              scroll->last_cur_dx = dx;
            }

          if (dy != 0)
            {
              if (should_reset_discrete_acc (dy, scroll->last_cur_dy))
                scroll->cur_dy = 0;

              scroll->last_cur_dy = dy;
            }

          scroll->cur_dx += dx;
          scroll->cur_dy += dy;
          dx = dy = 0;

          if (ABS (scroll->cur_dx) >= 0.5)
            {
              steps = trunc (scroll->cur_dx);
              if (steps == 0)
                steps = (scroll->cur_dx > 0) ? 1 : -1;

              scroll->cur_dx -= steps;
              dx = steps;
            }

          if (ABS (scroll->cur_dy) >= 0.5)
            {
              steps = trunc (scroll->cur_dy);
              if (steps == 0)
                steps = (scroll->cur_dy > 0) ? 1 : -1;

              scroll->cur_dy -= steps;
              dy = steps;
            }
        }
    }

  scroll->cur_unit = scroll_unit;

  if (dx != 0 || dy != 0)
    g_signal_emit (controller, signals[SCROLL], 0, dx, dy, &handled);
  else if (direction == GDK_SCROLL_SMOOTH &&
           (scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_DISCRETE) != 0)
    handled = scroll->active;

  if (direction == GDK_SCROLL_SMOOTH &&
      scroll->flags & GTK_EVENT_CONTROLLER_SCROLL_KINETIC)
    scroll_history_push (scroll, dx, dy, gdk_event_get_time (event));

  if (scroll->active && gdk_scroll_event_is_stop (event))
    {
      gtk_event_controller_scroll_end (controller);
      handled = FALSE;
    }

  return handled;
}

static void
gtk_event_controller_scroll_class_init (GtkEventControllerScrollClass *klass)
{
  GtkEventControllerClass *controller_class = GTK_EVENT_CONTROLLER_CLASS (klass);
  GObjectClass *object_class = G_OBJECT_CLASS (klass);

  object_class->finalize = gtk_event_controller_scroll_finalize;
  object_class->set_property = gtk_event_controller_scroll_set_property;
  object_class->get_property = gtk_event_controller_scroll_get_property;

  controller_class->handle_event = gtk_event_controller_scroll_handle_event;

  /**
   * GtkEventControllerScroll:flags:
   *
   * The flags affecting event controller behavior.
   */
  pspecs[PROP_FLAGS] =
    g_param_spec_flags ("flags", NULL, NULL,
                        GTK_TYPE_EVENT_CONTROLLER_SCROLL_FLAGS,
                        GTK_EVENT_CONTROLLER_SCROLL_NONE,
                        GTK_PARAM_READWRITE | G_PARAM_EXPLICIT_NOTIFY);

  /**
   * GtkEventControllerScroll::scroll-begin:
   * @controller: The object that received the signal
   *
   * Signals that a new scrolling operation has begun.
   *
   * It will only be emitted on devices capable of it.
   */
  signals[SCROLL_BEGIN] =
    g_signal_new (I_("scroll-begin"),
                  GTK_TYPE_EVENT_CONTROLLER_SCROLL,
                  G_SIGNAL_RUN_FIRST,
                  0, NULL, NULL,
                  NULL,
                  G_TYPE_NONE, 0);

  /**
   * GtkEventControllerScroll::scroll:
   * @controller: The object that received the signal
   * @dx: X delta
   * @dy: Y delta
   *
   * Signals that the widget should scroll by the
   * amount specified by @dx and @dy.
   *
   * For the representation unit of the deltas, see
   * [method@Gtk.EventControllerScroll.get_unit].
   *
   * Returns: %TRUE if the scroll event was handled,
   *   %FALSE otherwise.
   */
  signals[SCROLL] =
    g_signal_new (I_("scroll"),
                  GTK_TYPE_EVENT_CONTROLLER_SCROLL,
                  G_SIGNAL_RUN_LAST,
                  0, NULL, NULL,
                  _gtk_marshal_BOOLEAN__DOUBLE_DOUBLE,
                  G_TYPE_BOOLEAN, 2, G_TYPE_DOUBLE, G_TYPE_DOUBLE);
  g_signal_set_va_marshaller (signals[SCROLL],
                              G_TYPE_FROM_CLASS (klass),
                              _gtk_marshal_BOOLEAN__DOUBLE_DOUBLEv);

  /**
   * GtkEventControllerScroll::scroll-end:
   * @controller: The object that received the signal
   *
   * Signals that a scrolling operation has finished.
   *
   * It will only be emitted on devices capable of it.
   */
  signals[SCROLL_END] =
    g_signal_new (I_("scroll-end"),
                  GTK_TYPE_EVENT_CONTROLLER_SCROLL,
                  G_SIGNAL_RUN_FIRST,
                  0, NULL, NULL,
                  NULL,
                  G_TYPE_NONE, 0);

  /**
   * GtkEventControllerScroll::decelerate:
   * @controller: The object that received the signal
   * @vel_x: X velocity
   * @vel_y: Y velocity
   *
   * Emitted after scroll is finished if the
   * %GTK_EVENT_CONTROLLER_SCROLL_KINETIC flag is set.
   *
   * @vel_x and @vel_y express the initial velocity that was
   * imprinted by the scroll events. @vel_x and @vel_y are expressed in
   * pixels/ms.
   */
  signals[DECELERATE] =
    g_signal_new (I_("decelerate"),
                  GTK_TYPE_EVENT_CONTROLLER_SCROLL,
                  G_SIGNAL_RUN_FIRST,
                  0, NULL, NULL,
                  _gtk_marshal_VOID__DOUBLE_DOUBLE,
                  G_TYPE_NONE, 2, G_TYPE_DOUBLE, G_TYPE_DOUBLE);
  g_signal_set_va_marshaller (signals[DECELERATE],
                              G_TYPE_FROM_CLASS (klass),
                              _gtk_marshal_VOID__DOUBLE_DOUBLEv);

  g_object_class_install_properties (object_class, N_PROPS, pspecs);
}

static void
gtk_event_controller_scroll_init (GtkEventControllerScroll *scroll)
{
  scroll->scroll_history = g_array_new (FALSE, FALSE,
                                        sizeof (ScrollHistoryElem));
  scroll->hold_timeout_id = 0;
}

/**
 * gtk_event_controller_scroll_new:
 * @flags: flags affecting the controller behavior
 *
 * Creates a new event controller that will handle scroll events.
 *
 * Returns: a new `GtkEventControllerScroll`
 */
GtkEventController *
gtk_event_controller_scroll_new (GtkEventControllerScrollFlags flags)
{
  return g_object_new (GTK_TYPE_EVENT_CONTROLLER_SCROLL,
                       "flags", flags,
                       NULL);
}

/**
 * gtk_event_controller_scroll_set_flags:
 * @scroll: a `GtkEventControllerScroll`
 * @flags: flags affecting the controller behavior
 *
 * Sets the flags conditioning scroll controller behavior.
 */
void
gtk_event_controller_scroll_set_flags (GtkEventControllerScroll      *scroll,
                                       GtkEventControllerScrollFlags  flags)
{
  g_return_if_fail (GTK_IS_EVENT_CONTROLLER_SCROLL (scroll));

  if (scroll->flags == flags)
    return;

  scroll->flags = flags;
  g_object_notify_by_pspec (G_OBJECT (scroll), pspecs[PROP_FLAGS]);
}

/**
 * gtk_event_controller_scroll_get_flags:
 * @scroll: a `GtkEventControllerScroll`
 *
 * Gets the flags conditioning the scroll controller behavior.
 *
 * Returns: the controller flags.
 */
GtkEventControllerScrollFlags
gtk_event_controller_scroll_get_flags (GtkEventControllerScroll *scroll)
{
  g_return_val_if_fail (GTK_IS_EVENT_CONTROLLER_SCROLL (scroll),
                        GTK_EVENT_CONTROLLER_SCROLL_NONE);

  return scroll->flags;
}

/**
 * gtk_event_controller_scroll_get_unit:
 * @scroll: a `GtkEventControllerScroll`.
 *
 * Gets the scroll unit of the last
 * [signal@Gtk.EventControllerScroll::scroll] signal received.
 *
 * Always returns %GDK_SCROLL_UNIT_WHEEL if the
 * %GTK_EVENT_CONTROLLER_SCROLL_DISCRETE flag is set.
 *
 * Returns: the scroll unit.
 *
 * Since: 4.8
 */
GdkScrollUnit
gtk_event_controller_scroll_get_unit (GtkEventControllerScroll *scroll)
{
  g_return_val_if_fail (GTK_IS_EVENT_CONTROLLER_SCROLL (scroll),
                        GDK_SCROLL_UNIT_WHEEL);

  return scroll->cur_unit;
}
